The usual approach to generating random number distributions is to transform one or more standard uniformly distributed independent random numbers into one or more random variables with a given distribution. Many of these rely on heavy amounts of computational ability, such as is available on a PC and are thus not practical for use in devices, such as cell phones or other small relatively portable devices.
Random number generators can also be created in a purely hardware environment thereby bypassing the need for large storage or CPU capability. A particular type of digital electronic circuit known as a Linear Feedback Shift Register (LFSR) can be used to create a range of “random” values called Pseudo Random Binary Sequences, (PRBS). The properties of these circuits are well known, and their direct output is a Binomial Distribution, the discrete time equivalent of the Poisson Distribution. However, in applications where specific, and possible changing, distribution shaping is required, PRBS's are not adequate. For example, in situations with limited processing power, i.e. pure hardware digital circuitry with little or no access to a microprocessors, the range of random numbers available for use can be severely limited, both in the type of the distribution, and the range of statistical properties within the same distribution type, i.e. minimum, maximum, mean and standard distribution. The available “length” of any sequence may be severely limited before the sequence starts repeating from the beginning. This may lead to situations where the randomness is violated for decent results in the application of interest.